The Apas Association is restricted to the Semporna Peninsula, where it occurs:
extensively north of Tawau, in the catchment of the Sungai Apas,
north,
to the south of the river in the upper Kalumpang valley.
Parent materials comprise andesitic and dacitic lavas and ashes, which have been dissected into ridges with short steep slopes separated by narrow valleys up to 45 m deep.